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Thread started 06 Feb 2008 (Wednesday) 21:30
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Teleconverter/Lens Combinations

 
John ­ Sheehy
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Mar 16, 2014 09:09 |  #331

Canonised wrote in post #16757223 (external link)
Agree that we are always talking about FOV regardless of focal length of lens. I think the industry had no choice but to talk about 35mm equivalent because there is nothing else to compare with that makes sense. So the focal length of a 800 mm lens on a 1.6 cropped sensor has a focal length of 1280mm ("35mm equivalent").

Cropping does not change the focal length. Maximum FOV is the same as 1280mm on a FF. I don't see why anyone needs to actually call the lens' focal length anything different than what is written on it. Whether I use my 6D or my Pentax Q on my 400mm or 600mm lenses, they are still 400mm and 600mm. I know what 400mm means on all 3 sensor sizes that I use with my 400mm lenses.

I see it like this; you have a lens with certain properties; you put a sensor behind it to capture a rectangle of a certain size in its projection. Within that sensor, you have a certain pixel density (and microlenses, and a possible AA filter) to resolve it. The lens is what it is, and the sensor is a tool to capture part of its projection. Capturing a smaller rectangle does not increase focal length, does not increase "reach", and does not increase captured subject detail; higher pixel density, however, does do the latter.

Two photographers standing next to each other are both shooting the same subject with the same 500mm lens; one with a D30 and one with a 5D3. The person with the D30 brags that he is shooting with more reach, with more magnification, and at a greater effective focal length. All three, however, are pure nonsense, and given the same technique, the person with the 5D3 will be getting better detail of the subject, with 1.65x the linear resolution, and 2.75x as many pixels on the subject.

IF the sensor quality megapixel etc are of the same quality with the FF model. Currently the 5d2 is 21mp and 7D is 18mp.

Focal length has nothing to do with sensor size or density, or whether or not you crop in software. Focal length describes how far behind the front element a subject at infinity is in focus; period.

IF the 7Dmk2 has the rumoured 22 or 24 mp with same quality as the 5D3,

It is possible that it has the same noise levels per unit of sensor area. Having the same noise at the full image level would almost be science fiction come true.

I would tend to agree that there is a technical telephoto reach of 1280mm.

"Reach" is another hollow term, IMO. I do not use it (except when discussing it as a concept). What percentage of a frame a subject fills isn't even significant in regards only to the viewfinder, because not all viewfinders have the same AOV. What good would it do if your subject was half as high as the viewfinder frame, but the AOV was a narrow tunnel? The word "reach" implies a change of perspective. True reach would be a lens that was 100 feet long and you placed the front element in front of the subject, 105 feet away. Otherwise, you are not "reaching", but magnifying, or just cropping.

In all practical terms if both cameras (5d3 and 7d2) took the same picture with the same lens and printed out their files - even at A3 size. They will be the same quality but one is more magnified than the other.

You did not say if it was from the same distance, or if it was the the same filling of the full frame from different distances. Getting the same composition with the full-frame is impossible with the same optics, because the perspective will be different. From the same distance, the camera with the smaller pixels will get more detail, but if the 7D2 does not improve on read noise compared to the 7D, then there will be more subject-level noise at high ISOs (but less at base ISO to about 500, 250 with HTP).

I think the closest apology I can imagine is the comparison to car engine capacities. If a car has 1600cc and outputs 100 hp, adding a turbo charger does give you added hp and makes it faster but it does not change the engine capacity. Downside is the fuel consumption and engine wear. Just like drop in f stop when using TCs

The increase in f-stop with a TC is irrelevant as far as potential SQ (subject quality) is concerned. The subject gives less absolute exposure (light per unit of sensor area), but it cancels that out by having the subject cover more sensor area, so the loss of subject photons is minimal, and only a small amount due to small t-stop factors in the converter. What the TC does do, however, is make AF more difficult or impossible, as f-stop directly rules the day with phase-detect AF. Going to a higher ISO to use a TC at the same shutter speed can actually decrease noise, especially in a Canon DSLR at low ISOs, where an ISO 100 subject without a TC will have more read noise with normalized subject size, as would ISO 400 and a 2x TC. At higher ISOs, you don't have the gains in subject noise levels, but you still have finer Bayer CFA artifacts, and finer "pixel crud" in general; all images whether from a 7D with a strong AA filter, or a Sigma SD9 with its virtual point sampling, all look defective in one way or another at 100% pixel view on a coarse monitor. The more camera pixels you have of your subject, the better, as downsampling overcomes the camera's pixel crud, and leaves only the coarse monitor's display flaws.




  
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METAL1
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Mar 16, 2014 09:22 |  #332

patrickf117 wrote in post #16757266 (external link)
^^ Clean and sharp :cool: here ^^

THX :) i was really close!!


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shutterpat
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Mar 16, 2014 13:39 |  #333

40D + EF 400mm f/2.8L II USM + 1.4xII

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Aronis
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Mar 17, 2014 12:43 |  #334

Sheehy,

I enjoyed reading your above statement.

I have marveled at the claim of "more reach" for years! I have shot with a 10D for 10 years with a 28-70 and never considered the camera to have more 'reach' but rather the smaller censor just auto crops the full field of view of the lens. I show with a 35 mm film camera with the same lens (EOS1) and was scanning negatives as my digital approach at that time. Now with the same lens and a 1Dx if I crop the image (greater pixel density full frame sensor 10 years newer technology) on the Mac I can recreate that same "Reach" LMAO.....

Great discussion, and your comments are spot on.

Mike


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Mar 17, 2014 23:39 |  #335

40D + EF 400mm f/2.8L II USM + 1.4xII

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Mar 18, 2014 23:35 |  #336

40D + EF 400mm f/2.8L II USM + 1.4xII

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Mar 19, 2014 11:42 |  #337

40D + EF 400mm f/2.8L II USM + 1.4xII

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Mar 20, 2014 14:33 |  #338

40D + EF 400mm f/2.8L II USM + 1.4xII

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Mar 20, 2014 14:35 |  #339

600mm+1,4 ext & 1dx

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Sibil
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Mar 20, 2014 16:42 as a reply to  @ dioladetus's post |  #340

^^^^^
wow, awesome shot.




  
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Mar 22, 2014 09:09 |  #341

1DMKII + 300 f4L IS + 1.4xII <----

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Mar 22, 2014 09:20 |  #342

ShotByTom wrote in post #4888008 (external link)
Wow! Great shots! I've heard nothing good about the 2x extenders, now I want one!

They work well on the big whites 400mm f/2.8, 500mm f/4, 600mm f/4 and 800mm f/5.6


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John ­ Sheehy
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Mar 22, 2014 10:35 |  #343

butterfly2937 wrote in post #16777190 (external link)
They work well on the big whites 400mm f/2.8, 500mm f/4, 600mm f/4 and 800mm f/5.6

There are very different ways to evaluate the value of TCs. The most common way is for people to look at images at 100% view on their monitor with and without TCs, and in general, many lenses except the very sharpest will disappoint.

The way I see the use of a TC is that you have a longest lens that you are willing or able to use, and a TC is used to put the subject over more pixels. You would compare an upsized image with no TC, to an image with a TC, both with the subject displayed at the same size. The benefits of being spread over more pixels can easily outweigh slight losses of contrast, or mild haloing.

So, to me, there are good TCs, and not-as-good TCs, and any lens is worth using a good TC on if you can get the lens focused on the subject fast enough (with slower AF or manual focus). The optimum thing would be to have a sensor with smaller pixels and maybe even smaller physical size to maintain shooting speed, but Canon doesn't seem to be interested in sensors smaller than APS-C for EOS bodies, and their APS-C cameras lag way behind their FF cameras in read noise levels per unit of sensor area, so we are forced to use bigger sensors with TCs.




  
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John ­ Sheehy
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Mar 22, 2014 10:37 |  #344

Aronis wrote in post #16764976 (external link)
Sheehy,

Great discussion, and your comments are spot on.

Thank you. Sometimes I think I'm writing for myself here, but if I think I have a better way to look at something, I like to share it.




  
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butterfly2937
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Mar 22, 2014 15:58 |  #345

John Sheehy wrote in post #16777328 (external link)
There are very different ways to evaluate the value of TCs. The most common way is for people to look at images at 100% view on their monitor with and without TCs, and in general, many lenses except the very sharpest will disappoint.

The way I see the use of a TC is that you have a longest lens that you are willing or able to use, and a TC is used to put the subject over more pixels. You would compare an upsized image with no TC, to an image with a TC, both with the subject displayed at the same size. The benefits of being spread over more pixels can easily outweigh slight losses of contrast, or mild haloing.

So, to me, there are good TCs, and not-as-good TCs, and any lens is worth using a good TC on if you can get the lens focused on the subject fast enough (with slower AF or manual focus). The optimum thing would be to have a sensor with smaller pixels and maybe even smaller physical size to maintain shooting speed, but Canon doesn't seem to be interested in sensors smaller than APS-C for EOS bodies, and their APS-C cameras lag way behind their FF cameras in read noise levels per unit of sensor area, so we are forced to use bigger sensors with TCs.

All true. I use my 2x III with my 300mm f2.8 IS and my 600mm f/4 IS II. I shoot with a 1D4 and a 7D. I hope canon really amazes us with the 7D II. I was so hoping to see another 1.3 sensor as I just love my 1D4.


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